The study describes the results of a series of comparative experiments aimed at determining the differences in the ability to collect bacteria and fungi colonies by seven different impaction air samplers. The tests were performed simultaneously under identical environmental conditions in a \u201cclean\u201d room routinely used for cell culture or in a biochemistry room generally used for chemical experiments in the microbiological research laboratory of the University of Milan. The air flow in the rooms was switched-off for all the time of the experiments. The seven different air samplers were positioned on a cart, side by side, and operated simultaneously to collect 1m3 of atmosphere each. The results demonstrated that the numbers of airborne microorganisms impacted on TSA-containing Petri dishes, and grown as single colonies (CFU/m3), were different for each air sampler, although the difference was not statistically significant. Head to head tests were also performed with two identical TRIO.BAS apparatuses calibrated to 100 or 200 litres of aspirated air per minute. This test aimed at determining if a shorter aspiration time could negatively influence the cell viability and/or the bacterial concentration in the bioaerosol, as determined by counting the number of CFU/m3. The data ruled out this possibility and suggest that an aspiration time of 200 litres per minute might save time, especially when a repeated air sampling is mandatory for the control of sterility in virology laboratory \u201cclean rooms\u201d, pharmaceutical manufacturing areas and surgical rooms in the hospitals
